1. Field of the Invention
The present invention relates to trailer safety devices, and more particularly to a high lock warning system for fifth wheel hitches that alerts the operator of a truck being hitched to a semi-trailer in the event that the king post of the trailer passes over the fifth wheel plate of the towing vehicle, i.e., a “high lock” condition.
2. Description of the Related Art
Larger trucks, i.e., the tractors of tractor-trailer combinations, are universally equipped with “fifth wheel” type hitches comprising a large, heavy steel plate having a rearward oriented guide slot and a receptacle for the mating hitch component (“king pin”) of the trailer. Fifth wheel hitches enable the towing vehicle to tow a larger trailer than most other types of hitches will permit by supporting a large percentage of the weight of the trailer upon the rear of the towing vehicle. This type of hitch has also been scaled down for installation in smaller vehicles, such as pickup trucks and the like, for towing lighter trailers that are still relatively large and heavy for the size of the towing vehicle.
The trailer is hitched to the towing vehicle by backing the rear portion of the towing vehicle beneath the forward portion of the trailer until the king pin contacts the fifth wheel plate. Normally, the king pin will slide up the rearward facing slot of the fifth wheel plate and drop into the receptacle in the center of the plate, where a retaining mechanism captures the end of the king pin to hold it positively in place.
However, a potential problem can occur if the king pin of the trailer misses the receptacle in the center of the fifth wheel. The operator of the towing vehicle cannot see whether the king pin is properly engaged or not; he or she must operate by feel and sound to detect the dropping of the king pin into the fifth wheel receptacle. In the event that the fifth wheel plate slides past the king pin without engaging, the forward edge of the fifth wheel plate may pass completely beyond the king pin during the backing maneuver of the towing vehicle. When this occurs, the king pin may drop over the forward edge of the fifth wheel hitch plate, giving the vehicle operator the impression that the hitching maneuver has been accomplished successfully. This is known as a “high lock” when it occurs, and it will be seen that it is not a truly hitched condition between the towing vehicle and the trailer. If the operator drives forward in such a high lock condition, the king pin of the trailer will very soon slip around the forward edge of the fifth wheel plate, with the trailer detaching from the towing vehicle with disastrous consequences.
Thus, a high lock warning system for fifth wheel hitches solving the aforementioned problems is desired.